Hi razz,
Dont waste your money,the only way you can measure the AFR is before the cat, thats what the lamda sensors job is , the kev mod is very clever by telling the ECU that its colder than the ambient air temp actually is, and as the AFR is only going to be richer there will be no chance of any engine damage (as in running lean) no 2 engines are the same , so i would just play with the variable resister settings out on the road untill you think the engine feels sweet.

Hope this saves you some money

Vtec